Gas Spring Design Calculations

[Melissa Alvarado]

Accurateand effective spring design can only be accomplished in today's world using computer programs capable of running hundreds of simultaneous calculations. Following are just a few of the most basic formulas for getting a head start on compression spring design. Call us for design assistance. We can run a thorough analysis and assist you in designing the best spring for your application or download our ebook to get started.

When designing a spring, if possible, one spring should be designed so that the conditions can be met,

but if the design conditions simply cannot be met by one spring, sometimes the design conditions are met by combining multiple springs.

There are two ways to combine springs: a series method that stacks the springs vertically and a parallel method that arranges them horizontally. Such a classification applies not only to compression springs, but also to disc springs and other types of springs, which are similarly used in series or parallel combinations. From the viewpoint of load, the combination method in which the forces acting on each spring are equal is called series, and the combination method in which the displacement of each spring is equal is called parallel.

An example of using three compression springs is shown by the fig1. When the spring constant of n springs is Kn (k1, k2, and so on), the total spring constant (K) when these springs are combined in parallel and series is given by the following formula.

In parallel combination, the overall spring constant increases as the number of compression springs increases, whereas in series combination, the overall spring constant decreases as the number of compression Springs increases.

We mentioned that for parallel combination, the springs are arranged side by side, but this will take up space if you simply arrange them this way and so it is common to combine the springs internally and arrange them concentrically as shown in Fig2. This is sometimes called the main and sub springs. The lower, longer spring is called the main, and the upper, shorter spring is called the sub spring.

However, in the case of concentric combinations, it is necessary to alternately change the winding direction or to secure a certain gap between the springs so that the springs do not get entangled.

Also, by devising a combination of springs, it is possible to create nonlinear spring characteristics as shown in the figures a and b below.

For example, in the event the spring characteristics shown in Fig3 are required, it is necessary to combine springs with different free lengths or solid loads in series. The spring characteristics shown in Fig4 can be obtained by inserting a spring into the mechanism shown in Fig5 and making a combination of [upper spring constant] The accumulation and release of energy as shown in (a), (b), and (c) of Fig6 when load is applied and removed, generally passes through the same load-displacement curve (straight line), and so all the energy accumulated by applying a load is released in the process of removing the load. However, in the case of a spring characteristic with a hysteresis loop as shown in Fig6 (d), the energy of the area surrounded by the loop is consumed in one cycle from when the load is applied to when the load is removed.

When a spring is subject to a load, deformed, or a force is applied and the force is removed, the spring vibrates. The frequency of this vibration differs depending on the spring, and each has its own unique frequency. When the mass of the spring itself is m, its natural frequency (f) can be represented as follows.

As the spring mass (ms) is often smaller than the mass (m) of the object, it is generally considered to be β = 0. However, when the mass of the spring must be considered, it can be approximated as β = 0.49 in Fig9 or β = 0.37 in Fig10.

When designing a spring, it goes without saying that the spring constant is important, but it is often the case that this natural frequency must also be taken into consideration.

Here, M is the mass of the collision side, v0 is the collision speed, Pmax is the maximum collision force, and δmax is the maximum displacement on the collision side. The value of η is between 0 and 1. In an ideal case, it is 1, but in that case, the collision efficiency (η) of a spring with a fixed spring constant is 1/2.

When a shaft load is applied to an elongated column, a phenomenon occurs in which the column is suddenly displaced laterally.

This is called buckling.

The load when buckling occurs is called the marginal buckling load.

Also, compression springs buckle when compressing to a certain height if large aspect ratio(Ratio of free height to mean coil diameter).

Buckling of the compression spring does not essentially change from buckling of long column.

By equivalently replacing the compression spring with one pillar on the coil center line, it is possible to analyze in exactly the same way as in the long column.

However, in the case of compression springs, it is necessary to take into account the effects of shear deformation and the change in length of the spring which could be ignored with the long pillar.

According to a strict analysis that takes into consideration the helical structure of the spring, these effects are small with the springs usually used, so this equation is considered practical in practice.

Conpower and power springs are used in many applications where torque is required. Some well-known examples are clocks, toys, seat belts, canister vacuum cleaners, dog leashes and badge reels. To meet varying design demands, many parameters must be defined to gain enough information to begin.

This value is essential to determining the maximum width of the spring steel. We need to know how high the case can be in the event that we need to maximize the spring material to achieve the required torque. The spring case often does not need to consume all of the available space, but we can suggest a spring to fit if the design is already determined.

The arbor is located in the center of the case. The inside of the spring will attach to this arbor, and the arbor diameter will help determine the space inside the case, the number of available turns, and spring and case size.

Torque is not the pull force on a cable. Torque is the rotational force exerted when the spring is unwinding. Friction causes hysteresis in a power spring, meaning that a greater torque is required to wind the spring than it will provide when unwinding.

A cycle is defined as one full winding of the material and one unwinding of the material. Power springs rarely have life cycles exceeding 200,000 winds and will likely be under 100,000 if space and torque are optimized.

There are many other options and factors to discuss when working with power springs and Conpower springs. This information is a good starting point for understanding the many areas of concern during the power spring design process. Please consult your Vulcan Spring Product Manager early in the design process to understand your unique needs and achieve the most efficient results.

Compression springs are very common and used in a broad range of applications. Characterized by an open-coil helical form, compression springs offer resistance to axially applied force. In essence, when force is applied on a compression spring, it pushes back. This occurs because the spring is designed to return to its original resting state when pressure is applied.

Compression springs have a simplistic appearance, so it is common to overlook the fact that specific design intentions have been carefully implemented. In reality, compression springs require careful calculations and the combination of a wide range of engineered elements to fulfill the purpose of their design.

These calculations relate to spring force or spring rate, spring index, and various dimensional tolerances. Careful consideration of the length of wire, the overall outside diameter (OD), inside diameter (ID) of the coil, and the stress tolerances it can handle are all critical to ensure the end product will function as intended.

Compressions springs are typically manufactured by feeding wire stock into an auto-coiler. Individual springs or small production runs can be coiled using a lathe, but this practice has gone out of use due to safety concerns for the operator. Auto-coilers are highly versatile and can typically be adjusted to alter the major factors of the spring, such as length, number of coils, or coil tension.

Various environmental factors and manufacturing processes influence material selection. Each wire type can contribute specific properties, which impact performance, manufacturing, and longevity of the spring. The following wire materials are used in compression springs:

At Southern Spring & Stamping, Inc., we have more than 60 years of experience in the manufacture of compression springs. Our team uses advanced Computer Numerical Control (CNC) machinery to form wire into compression springs, providing superior precision and high repeatability.

Our material selection allows our clients to make the most cost-effective material choices for their operation. Our facilities are ISO 9001:2015 certified and we adhere to a comprehensive list of industry standards, including:

Compliance with these standards provides documented proof of our commitment to quality, productivity, reduced costs, and low defect rates, and increased customer satisfaction. We offer prototyping and design support and can handle production runs of all sizes.

Spring rate can be measured by taking the difference in force at 80% maximum deflection and 20% minimum deflection and dividing by the difference in deflection. The spring rate tends to be constant over the central 60 percent of the deflection range. Because of end-coil effects, the first 20% of deflection range has a considerably lower spring rate. The final 20% of deflection shows considerably higher spring rate. When designing for a particular spring, design for critical loads and rates to be within the central 60% deflection range. Standard and custom springs are available.

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